Estimated coal stockpiles at U.S. electric power plants in March 2012 (latest EIA data available) were about 196 million short tons, almost 18% above the level in March 2011 and above the five-year range. Coal stockpiles are up as a result of declines in coal consumption by electric power plants.

One measure of the disposition of coal stocks, called days of burn, is an estimate of how many days a stockpile of coal would last at a plant based on past consumption patterns. This measure creates a forward-looking estimate of coal supply at a power plant. Days of burn in February 2012 were at their highest levels since 2008, when EIA began computing the statistic. Days of burn in March 2012 were slightly below the February levels, reaching a national average of 91 days of burn. Mostly for reliability reasons, plant operators maintain stockpiles within certain ranges (usually about 50 to 80 days) even though coal supply disruptions of that duration are relatively unlikely.

Coal-fired generators are using various commercial strategies to manage their growing coal stockpiles, including:

Not accepting additional purchases of coal by executing a contractual procedure known as force majeure. For example, GenOn, a merchant generator, described its invocation of force majeure in a recent quarterly filing with the Securities and Exchange Commission due to a lack of physical space to store additional coal receipts.

Deferring purchases of coal to later years in a long-term contract. Consequently, some generators are then dispatching natural gas-fired units ahead of coal-fired units or using other hedges against further price fluctuations in coal markets.